Dosage and Frequency
Time to Steady State
First-Line Maintenance Antiepileptic Drugs
Adjust dosage in all species by monitoring serum levels and seizure diary.
Dogs: 2–4 mg/kg, PO, bid (starting dose); up to 10 mg/kg, bid
40–90 hr (Beagles 25–38 hr)
15–45 mcg/mL (66–200 μmol/L), preferably keep values within 20–35 mcg/mL (85–150 μmol/L)
Sedation, polydipsia, induces P450 system, increase in alkaline phosphatase common; liver failure is possible but uncommon.
Cats: 2–4 mg/kg, PO, bid (starting dose)
Liver enzymes do not typically increase in cats.
Horses: 3–5 mg/kg/day, PO, as a starting dose; up to 11 mg/kg/day, PO
10–40 mcg/mL (43–175 μmol/L)
Foals: as above
Ruminants: 11 mg/kg/day, PO
Bromide (potassium salt)
Dogs, cats: 20–40 mg/kg, PO, once daily or divided bid if GI upset. Caution using bromide in cats (see comments).
Dogs: loading dose 400–600 mg/kg, PO divided into 4 doses, given over 1–4 days
Horses: 90 mg/kg/day, PO
Dogs: 20–46 days
Cats: 10 days
Horses: 5 days
Dogs: 100–200 days
Cats: 6 wk
Bromide alone: 1–3 mg/mL (15–20 μmol/L)
Bromide/phenobarbital combined: 1–2 mg/mL
Sedation, weakness, polydipsia, vomiting, polyphagia, skin rash. Reduce dose with renal insufficiency. High chloride intake increases bromide elimination. Chloride content of diet should be stable. Use with extreme caution in cats and monitor with thoracic radiographs because bronchial/asthmatic signs may be fatal in cats.
Bromide (sodium salt)
17–30 mg/kg, PO, once daily or divided bid if GI upset. The dose of sodium bromide is less than that of potassium bromide to account for the higher bromide content.
See potassium bromide comments.
Cats: 0.25–0.5 mg/kg, PO, bid-tid
While oral diazepam is not effective as maintenance AED in dogs, it can be used in cats as a maintenance AED. Sedation and liver failure are potential problems in cats.
Second-Line (Add-on) Antiepileptic Drugs for Dogs
Dogs: 0.1–0.5 mg/kg, PO, bid-tid
Extremely potent benzodiazepine; sedation; withdrawal signs if drug stopped abruptly.
Dogs: 0.5–1 mg/kg, PO, tid
15 times less potent than clonazepam; sedation; withdrawal seizures. Can increase phenobarbital concentration.
Dogs: 15 mg/kg, PO, tid; increase by 15 mg/kg biweekly until seizures controlled; maximal (toxic) dosage 300 mg/kg
Nervousness, keratoconjunctivitis sicca, mild thrombocytopenia, leukopenia; induces P450 system; liver disease. Use with care with other potentially hepatotoxic drugs.
Dogs: 10 mg/kg, PO, tid; up to 30–60 mg/kg, tid
4–16 mg/La (70–120 μmol/L)
Sedation, dizziness, ataxia, fatigue, diarrhea; reduce dose with renal dysfunction.
Dogs: 20 mg/kg, PO, tid
Restlessness, vomiting, ataxia at dosages >400 mg/kg/day
Dogs: 5–10 mg/kg/day, PO, bid
2–25 mg/L (15–60 μmol/L)a
GI upset, irritability
Dogs: 10–60 mg/kg, PO, tid
Probably ineffective due to very short half-life; liver, alopecia, and pancreatitis; vomiting usually avoided by giving drug with food.
Dogs: 5 mg/kg/day, PO, bid, if phenobarbital is not concurrently given; 10 mg/kg, PO, bid if phenobarbital is concurrently administered.
10–40 mg/L (45–180 μmol/L)
Sedation, ataxia, loss of appetite. Potential adverse effects (eg, keratoconjunctivitis sicca, bone marrow dyscrasia, hepatopathy, vasculitis, and metabolic acidosis) could occur because of sulfonamide base.
a Therapeutic range established for people